The administration of liquids parenterally to a patient is a treatment that has been employed for many years. It typically involves the use of a container of liquid to be infused, an elongated flexible tube for conveying the liquid from the container to a patient and a cannula or catheter for insertion into the cardiovascular system of the patient to introduce the liquid for infusion into the patient. A variety of liquids may be infused in this manner, including dextrose, saline, Ringers solution, and water or any combination of these solutions. Others include whole blood plasma. More recently, drugs such as antibiotics, heprine, etc. are administered in this manner.
The most common manner of controlling the flow of the liquid being administered parenterally to the patient has been to selectively collapse a portion of the flexible delivery tube using a roller clamp, for example. The rate of flow in such cases is determined by the rate at which drops of liquid are observed falling through a drip chamber.
Gravity infusion of the parenteral solution is accomplished by suspending the solution container several feet above the patient and connecting the solution container to the venepuncture site via a disposable intravenous administration set which includes the drip chamber and flexible delivery tube U.S. Pat. No. 4,175,558 discloses an example of a roller clamp for collapsing the delivery tube to control the flow rate.
The roller clamp is a simple, two-piece plastic device that progressively compresses the plastic tube of the intravenous administration set at a single point on the tube thereby occluding the tube to create a pressure drop across the restriction and a corresponding reduction in flow rate. However, the use of such roller clamps is problematical due to cold flow or creep of the plastic tubing at the point of restriction, which causes the flow rate to decrease after setting. This circumstance requires repeated checking and resetting by the user.
Additionally, because the plastic tube is restricted at a single point by the roller clamp, high resolution of the flow rate of the fluid through the pinched orifice is difficult to achieve. That is, a very slight change in orifice size creates a large change in the flow rate.
Several flow rate regulators such as the Abbott Laboratories' Dial-A-Flow, see, U.S. Pat. No. 3,877,428, have been introduced in recent years in attempts to overcome the aforementioned disadvantages associated with the use of conventional roller clamps. While these known devices do provide more accurate control of the flow rate than the conventional roller clamp, they are multi-component devices which cost more than the actual intravenous administration set to produce.
Moreover, these known flow rate regulators usually incorporate an elastomeric seal. In high volume production, a small percentage of the flow rate regulators can experience leaks about their elastomeric seals. This prevents the positioning of these devices in an elevated position close to the intravenous administration set drip chamber since in that location a leak would admit air to the system and introduce the danger of emboli to the patient. Therefore, with these known flow regulators, the drip chamber and flow regulator are normally located in spaced relation. This makes it inconvenient for the user when setting the flow rate and monitoring the drip rate since these are accomplished at different locations.
The aforementioned known flow regulators of the type disclosed in U.S. Pat. No. 3,877,428 are based on the Poiseuille equation for uniform laminar, non-turbulent flow. That is, the flow rate control is achieved by changing the length of a fluid path of small cross-section. This manner of operation provides much better accuracy and resolution than the "orifice" type of operation employed in the conventional roller clamp application. The components of the flow regulators providing the small cross-section fluid path can be mass produced by plastic injection molding in a repeatable manner which results in consistent flow performance of these devices.